This invention relates to fuel storage systems and filling apparatus therefor. The use of propane as a fuel source for engines, including automobile engines, has become desirable due to the increased fuel economy which is often afforded by this fuel source. Propane as a fuel source for engines also has the advantage of allowing for decreased levels of undesirable exhaust emissions.
Due to the high thermal expansion coefficient of liquid propane, the overfilling of propane tanks is clearly dangerous. Expansion of the propane fuel can lead to leakage from the tank whereby gaseous and liquid fuel can accumulate under a vehicle equipped with a propane tank, thus posing a significant fire and explosion hazard. Also, in a situation where an extreme expansion occurs, for example where the tank is filled in sub-zero conditions and is subsequently stored in a hot environment, the expansion can lead to an explosion. To address the problem of thermal expansion, propane vehicle tanks now in use are usually single or double compartment vessels which are built to conform to existing pressure vessel design. Generally these tanks are filled to about 80% of the total capacity with the remaining 20% left vacant to allow for thermal expansion of the fuel.
Currently filling systems for these tanks allow propane gas to escape into the atmosphere during filling. When the 80% level is reached, these tanks expel liquid propane, at which time the operator doing the filling must immediately stop filling. In the event of overfilling the vehicle must be driven off to a safe area where the excess liquid fuel can be bled off. These systems are both ineffective and dangerous and lead to a source of environmental pollution.
One solution to these filling problems is the construction of a tank having a primary compartment and an expansion compartment which is smaller than the primary compartment. A valve assembly is constructed which allows expanded fuel to move from the primary compartment to the expansion compartment in order to relieve pressure in the primary compartment.
U.S. Pat. No. 5,411,058 issued to J. W. Walsh et al. on May 2, 1995 shows a fuel reservoir for a gaseous fuel made up of a primary compartment which is designed to be totally filled and a secondary compartment which is horizontally adjacent to the primary compartment and has very little vertical expansion space because of the specific tank configuration disclosed. A spring loaded pressure relief valve allows fuel to pass from the primary compartment to the expansion compartment when a specific pressure difference exists between the two compartments. Each compartment has an outlet through which fuel can be drawn. Hence, there are separate lines coming from each separate compartment which lead to the engine. A check valve is used to permit fuel to be drawn first from the expansion compartment and then from the primary compartment. This known system is quite complex as it is designed to provide both a liquid fuel and a gaseous fuel to the vehicle's internal combustion engine. This system has an integrated gaseous fuel control and handling unit.
Current propane fuel systems have the additional problem of having propane fuel trapped in the lines and fittings between the tank shut-off valve and the fuel lock-off. Expansion of the fuel leads to burst lines and fittings and the discharge of propane into the atmosphere.
In order to address this problem, pressure sensitive relief valves were commonly introduced between the tank valve and the lock-off. The valves are set to relieve the excess hydrostatic pressure by venting the propane into the atmosphere. This can lead to propane building up beneath the vehicle, which is very dangerous and environmentally offensive.